1. Field of the Invention
The present invention relates to balloons that are used in connection with catheters, and in particular, corrugated balloons that can be adapted for use with dilatation catheters and catheters used to deliver intraluminal stents.
2. Description of the Prior Art
Catheter systems were initially provided for use during embolectomy and dilatation procedures to access intraluminal clots, thrombus, emboli or other deposits that have built up in the vessel. In a traditional embolectomy procedure, a catheter having a latex balloon is inserted into the lumen of the blood vessel so that the balloon extends beyond the clot, thrombus or deposit. The balloon is then inflated and pulled out of the vessel, dragging the clot, thrombus or deposit out of the vessel. In a traditional dilatation procedure, a catheter having a balloon is inserted into the lumen of the blood vessel so that the balloon is positioned in the region of the thrombus, emboli or deposit. The balloon is then inflated to break up the thrombus, emboli or deposit, by pushing it into the vessel wall. The catheter and its balloon are then removed from the vessel.
Recently, the development of endovascular stents and grafts have introduced an additional important function for balloon catheters: to carry, deliver and deploy intraluminal prosthesis such as stents and stent-grafts (also referred to hereinafter as "prosthesis"). In such an application, the prosthesis is compressed around the exterior of a deflated balloon. The catheter is then delivered intraluminally until the balloon is positioned at the desired stenting location in the vessel. Thereafter, the balloon is inflated to expand the prosthesis until the prosthesis engages the luminal wall of the vessel. The balloon is then deflated, and the catheter removed.
Conventional balloons are made from a polymeric material, with the most common examples being polyethylene (PE), nylon, silicon, or polyethylene terephthalate (PET). These conventional balloons typically have a generally oval configuration when expanded, and have a smooth and flat exterior surface.
Balloons made from PE, silicone or similar materials tend to be more compliant than balloons made from PET and nylon. As a result, PET and nylon balloons are favored for use in the delivery of prostheses. However, PET and nylon balloons have very thin walls that tend to be susceptible to mechanical damage (e.g., scratching, punching, tearing) and which may result in leakage of the balloon.
While conventional balloons have performed their embolectomy, dilatation and prosthesis-delivery functions relatively effectively, there are still unresolved problems associated with the use of conventional balloons for these procedures.
For example, the compliance of conventional balloons is relatively consistent throughout, which can be troublesome in certain circumstances. For example, balloons made from PE material exhibit greater compliance under higher pressures. This may cause over-dilation of the blood vessel, and in extreme cases, may cause the blood vessel to rupture. Some conventional balloons may also experience radial tearing when the balloon is expanded.
In addition, when used for dilatation, the generally oval expanded configuration of the conventional balloon with a smooth and flat exterior surface may sometimes be ineffective in dilating certain calcified or hard deposits, if these materials are particularly hard. This is because expansion of a relatively compliant balloon against very hard deposits may not cause the deposit to be dislodged or broken apart from the luminal wall.
When used for the delivery of prostheses, there is a significant concern that the prosthesis that is compressed over the non-inflated balloon will slip from or become mispositioned along the exterior surface of the balloon. This slippage or mispositioning is again a potential by-product of the smooth and flat exterior surface of a conventional balloon. Therefore, endovascular delivery systems that are provided to deliver prostheses often provide mechanisms (e.g., sleeves for covering the ends of the prosthesis) for holding the prosthesis securely over the non-inflated balloon. These mechanisms often complicate the design of the delivery systems and increase the costs thereof.
In addition, effective deployment of the entire length of the prosthesis requires the balloon to have generally the same outer diameter throughout when expanded. In this regard, the normal oval configuration of an expanded balloon makes it difficult to achieve this objective. To address this problem, a number of efforts have been made, such as to provide longer balloons, and to provide balloons that are constrained at both ends to cause the balloon to assume a "square" configuration when expanded, among others. However, longer balloons complicate the design of the delivery system and catheter. In addition, balloons having constrained ends are susceptible to experiencing a "dog-bone" effect when expanded, where both ends of the balloon are wider than the central portion of the balloon, resembling the shape of a dog-bone. The "dog-bone" effect can be potentially dangerous to the patient because the ends of the expanded prosthesis tend to have a larger diameter than the central portions, and therefore may cut or otherwise rupture the wall of the vessel into which the prosthesis is being deployed.
Thus, there still exists a need for balloons that can be used effectively for both dilatation and the delivery of prosthesis, which help to reduce the complexity of catheter devices used for these procedures, which have a simple structure, and which are easy and inexpensive to manufacture.